The present invention relates to an image display apparatus permitting improvement in yield and in image quality.
A polycrystalline Si thin film transistor (TFT) having an offset canceler, using a source follower circuit configuration as a buffer amplifier, such as ones described in JP-A-11-73165 (corresponding to EP 0899714A2) and JP-A-10-301539, involves the following problems.
First of all, there is a problem that building in as many analog active circuits such as a buffer amplifier as signal lines pulls down the yield. Whereas buffer amplifiers are configured by monocrystalline Si transistors excelling in the uniformity of characteristics in an amorphous Si TFT panel, a polycrystalline Si TFT is susceptible to unevenness in characteristics due to many defect levels distributed in a channel, resulting in inevitable unevenness in the characteristics of the buffer amplifiers, and this pulls down the yield.
A second problem is the inferior capability of an offset canceler using a polycrystalline Si TFT to that of what is configured by a monocrystalline Si transistor. Since a polycrystalline Si TFT does not permit as fine machining as a monocrystalline Si transistor does, the parasitic capacitance of each switch of the offset canceler becomes inevitably large, and moreover the parasitic capacitances are more uneven. This directly leads to greater errors in the canceling output of the offset canceler, and invites, again directly, a poorer S/N ratio of image quality.